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Date:   Tue,  5 Apr 2022 22:45:55 +0100
From:   Alan Maguire <alan.maguire@...cle.com>
To:     andrii@...nel.org, daniel@...earbox.net, ast@...nel.org
Cc:     kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, Alan Maguire <alan.maguire@...cle.com>
Subject: [PATCH bpf-next 1/2] libbpf: improve string handling for uprobe name-based attach

For uprobe attach, libraries are identified by matching a ".so"
substring in the binary path.  This matches a lot of patterns that do
not conform to library .so[.version] suffixes, so instead match a ".so"
_suffix_, and if that fails match a ".so." substring for the versioned
library case.

For uprobe auto-attach, the parsing can be simplified for the SEC()
name to a single ssscanf(); the return value of the sscanf can then
be used to distinguish between sections that simply specify
"u[ret]probe" (and thus cannot auto-attach), those that specify
"u[ret]probe/binary_path:function+offset" etc.

Suggested-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
---
 tools/lib/bpf/libbpf.c          | 77 ++++++++++++++++-------------------------
 tools/lib/bpf/libbpf_internal.h |  5 +++
 2 files changed, 35 insertions(+), 47 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 91ce94b..3f23e88 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10750,7 +10750,7 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
 	const char *search_paths[3] = {};
 	int i;
 
-	if (strstr(file, ".so")) {
+	if (str_has_sfx(file, ".so") || strstr(file, ".so.")) {
 		search_paths[0] = getenv("LD_LIBRARY_PATH");
 		search_paths[1] = "/usr/lib64:/usr/lib";
 		search_paths[2] = arch_specific_lib_paths();
@@ -10897,60 +10897,43 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
 static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
 {
 	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
-	char *func, *probe_name, *func_end;
-	char *func_name, binary_path[512];
-	unsigned long long raw_offset;
+	char *probe_type = NULL, *binary_path = NULL, *func_name = NULL;
+	int n, ret = -EINVAL;
 	size_t offset = 0;
-	int n;
 
 	*link = NULL;
 
-	opts.retprobe = str_has_pfx(prog->sec_name, "uretprobe");
-	if (opts.retprobe)
-		probe_name = prog->sec_name + sizeof("uretprobe") - 1;
-	else
-		probe_name = prog->sec_name + sizeof("uprobe") - 1;
-	if (probe_name[0] == '/')
-		probe_name++;
-
-	/* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
-	if (strlen(probe_name) == 0)
-		return 0;
-
-	snprintf(binary_path, sizeof(binary_path), "%s", probe_name);
-	/* ':' should be prior to function+offset */
-	func_name = strrchr(binary_path, ':');
-	if (!func_name) {
+	n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%zu",
+		   &probe_type, &binary_path, &func_name, &offset);
+	switch (n) {
+	case 1:
+		/* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
+		ret = 0;
+		break;
+	case 2:
 		pr_warn("section '%s' missing ':function[+offset]' specification\n",
 			prog->sec_name);
-		return -EINVAL;
-	}
-	func_name[0] = '\0';
-	func_name++;
-	n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
-	if (n < 1) {
-		pr_warn("uprobe name '%s' is invalid\n", func_name);
-		return -EINVAL;
-	}
-	if (opts.retprobe && offset != 0) {
-		free(func);
-		pr_warn("uretprobes do not support offset specification\n");
-		return -EINVAL;
-	}
-
-	/* Is func a raw address? */
-	errno = 0;
-	raw_offset = strtoull(func, &func_end, 0);
-	if (!errno && !*func_end) {
-		free(func);
-		func = NULL;
-		offset = (size_t)raw_offset;
+		break;
+	case 3:
+	case 4:
+		opts.retprobe = str_has_pfx(prog->sec_name, "uretprobe");
+		if (opts.retprobe && offset != 0) {
+			pr_warn("uretprobes do not support offset specification\n");
+			break;
+		}
+		opts.func_name = func_name;
+		*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
+		ret = libbpf_get_error(*link);
+		break;
+	default:
+		pr_warn("uprobe name '%s' is invalid\n", prog->sec_name);
+		break;
 	}
-	opts.func_name = func;
+	free(probe_type);
+	free(binary_path);
+	free(func_name);
 
-	*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
-	free(func);
-	return libbpf_get_error(*link);
+	return ret;
 }
 
 struct bpf_link *bpf_program__attach_uprobe(const struct bpf_program *prog,
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index b6247dc..155702a 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -103,6 +103,11 @@
 #define str_has_pfx(str, pfx) \
 	(strncmp(str, pfx, __builtin_constant_p(pfx) ? sizeof(pfx) - 1 : strlen(pfx)) == 0)
 
+/* similar for suffix */
+#define str_has_sfx(str, sfx) \
+	(strlen(sfx) <= strlen(str) ? \
+	 strncmp(str + strlen(str) - strlen(sfx), sfx, strlen(sfx)) == 0 : 0)
+
 /* Symbol versioning is different between static and shared library.
  * Properly versioned symbols are needed for shared library, but
  * only the symbol of the new version is needed for static library.
-- 
1.8.3.1

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